1. Field of the Invention
The invention relates to an actuation device, particularly for the actuation of a high-speed circuit breakers, and which mainly consists of an armature acting strokewise and a holding magnet and an attracting magnet which are excited by one and the same electromagnetic source, the attracting magnet drawing the armature towards itself when a previously determined current value is exceeded.
2. The Prior Art
Devices of the kind as mentioned above are universally known. In fact, when using one and the same magnetic flux source for the excitation of both the holding magnet and the attracting magnet, the speed of motion of the armature can be made to be superior to that with systems in which the holding magnet and the attracting magnet are excited individually. With the latter mentioned systems, the armature will be traversed by two different fluxes, and as a result, it will become over-saturated. In this manner, the holding force is unfavorably affected and the braking action of the holding circuit will increase upon the armature travelling.
Owing to the armature becoming over-saturated, its magnetic resistance to the magnetic flux of the holding circuit will increase, as a result of which the magnetic flux will rather tend to close via the air gap, due to which the holding force will decrease.
In order to keep this holding force sufficiently high to retain the armature, the attracting force can be reduced, either by decreasing the attracting flux or by preventing part of the attracting flux from passing via the armature, or the armature can be made of a more robust construction so that it may become less saturated. All these solutions have the disadvantage that the speed of the armature is unfavorably affected, either owing to the attracting force being reduced, or to the mass of the armature being increased.
It is known that, devices with armatures can be constructed, in which use is made of a flux excited by one and the same magnetic current source, both for the holding magnet and for the attracting magnet see German Pat. Nos. 1.087.679 and 1.102.252. In these cases, however, two magnetic systems are applied, in which the magnetic fluxes act simultaneously and in the same way upon a common armature.
Although, in this manner, a rather complicated assembly was obtained, this was necessary in order to realize a symmetric distribution of the holding and attracting forces upon the armature.
Another disadvantage is that one of the two air gaps between the attracting magnet and the armature is not perpendicular to the lines of flux, but forms an angle with these lines of flux, as a result of which the attracting force of the attracting magnet and, consequently, also the speed of the armature cannot be optimal. Also, due to the angle, the decrease in resistance in the attracting circuit will not equal the increase in resistance in the holding circuit since a widening of the air gap between the armature and the holding magnet will not cause a proportional narrowing of the air gap between the armature and the attracting magnet. Yet another disadvantage is that the excited flux is divided into a part for the holding circuit and a part for the attracting circuit. Only after the resistance in the holding circuit will have attained a certain value due to the air gap, will the greater part of the flux be used for the attracting circuit. Meanwhile, however, the armature will have already started moving. Consequently, the magnetic flux as a result of the current appearing due to a breakdown or short-circuit cannot be fully used for the tripping action.
Besides, the magnetic fluxes are generated with the aid of windings, so that these will have to be dimensioned to the current to be anticipated while the repelling forces in the windings in case of a short-circuit should likewise be taken into account.